In a wireless network, communication apparatuses of the network generally communicate (with one another, and/or with other communication apparatuses) using radio transmissions that share the same transmission medium. Although such radio transmissions are normally configured to occupy allocated or assigned frequency bands (also called sub-channels, and which may be divided in time to form “chunks”), the radio-frequency spectrum is nevertheless shared by such transmissions.
Radio transmissions occupying the same parts of the shared communication spectrum can interfere with one another. The level of interference will depend on a number of factors, for example on the power levels of the respective transmissions, and on the relative locations of the transmitters. In fact, many factors have an impact on interference.
Considering a wireless network comprising base stations (BSs) as an example, these factors include antenna orientation in the BSs, transmission schemes employed (say FDD or TDD) by the BSs, the nature of sectorisation within the cells of the BSs, the power control schemes employed, the handover schemes employed, the nature of traffic being handled by the BSs at each point in time, and the number of active subscribers (e.g. user equipment, or UEs) assigned to each BS at each point in time. Any smart antenna scheme employed in the BSs may also affect interference. Considering the impact of transmission power on interference, it is possible that a BS may be assigned a number of separate sub-channels that may use different transmission power levels. These different power levels can affect interference. Another important factor is the interference leakage between two adjacent sub-channels. Although in telecommunications systems the practical solution is to introduce guard bands to reduce such leakage, the arrangements of sub-channels assigned to a BS can nevertheless affect interference. Other important factors regarding interference may be, for example, surrounding atmospheric conditions and the presence or absence of obstructions to signal propagation. The effect of interference can be signal degradation and an overall drop in system performance as a whole, as compared to that in an “interference-free” system. It is therefore desirable to manage spectrum allocation to BSs within such a network, particularly among BSs located physically close to one another relative to other BSs. For this purpose, the concept of a “cluster” (see below) may be used to associate plural BSs in a network. BSs in a cluster are usually, but not always, in a single geographical region of the network.
Spectrum allocation within BSs of a cluster is a relatively small-scale and localised process, but it can be viewed as part of a hierarchy of spectrum allocation procedures with higher-level allocation being performed at network level and even at an inter-network level. This is particularly the case when a plurality of wireless networks co-exist, in other words operate at the same time in adjacent or overlapping geographical areas, and frequency spectra. Such multiple networks may be considered as parts of an overall or total wireless communication system in a geographical region of interest. Efforts are currently being made to improve the abilities of such multiple networks to co-exist and coordinate themselves; for example the so-called WINNER project.
The concept of a “gateway” used in WINNER is relevant to the invention to be described, and so the concept of co-existing networks will be briefly explained by way of background information.
FIG. 1 shows one way in which multiple networks can be coordinated. Here, an overall system is constituted by a number of wireless networks (here called Radio Access Networks or RANs) RAN1, RAN2 and RAN3 which each comprise a Gateway GW for the purpose of accessing the individual wireless network from a higher Core Network CN 6, typically via an IP Network. As proposed in WINNER for example, the GW is responsible for long-term spectrum assignment (see below) and for at least part of the radio resource management (RRM) in its own network. It is assumed that one GW is assigned for each wireless network.
Each wireless network may also comprise one or more Base Stations (BS) exemplified in the Figure by BS1, BS2, BS3, each of which is connected to at least one GW. Each such BS may transmit (and receive) radio signals to (and from) one or more User Equipments (UEs), within its geographical area of coverage (often referred to as a “cell”). UEs may also be referred to as user terminals (UTs), terminal equipments (TEs) or Mobile Stations (MSs). Since both base stations and user terminals are equipped to transmit and receive signals over one or more of the wireless networks, they are sometimes referred to below collectively as transceivers. As explained in more detail below, base stations and their UEs may be grouped into “clusters” extending over one or more adjacent or even non-adjacent cells, for spectrum allocation purposes.
Communications between the CN, GWs and BSs may be across wired communication links (e.g. via fiber-optic links) or across wireless communication links (e.g. across radio or microwave links). As indicated by arrows in FIG. 1, the GWs communicate among themselves, for example for the purpose of long-term (LT) spectrum assignment, as will be explained later. Meanwhile, the BSs communicate among themselves for, among other things, short term (ST) spectrum assignment as will also be explained below. Communications between the BSs and the UEs are typically across wireless links.
The CN may be distributed, for example across the IP network. The IP network may, for example, include the Internet. Although three networks (RANs) are shown in FIG. 1, the network may include any number of such RANs. Similarly, each wireless network may have any number of GWs, BSs and UEs. The UEs may be mobile and move from the cell of one BS to that of another BS, and even from one RAN to another RAN. The BSs may be dedicated to a particular wireless network, or may be shared between them on a temporary or non-temporary basis. One BS may for example serve two wireless networks at the same time. Although the wireless networks in FIG. 1 are made up of the same component apparatuses, they may employ different radio access technologies. Typically, different networks may be operated by different mobile-network operators. Different networks and BSs may have separate geographical areas of coverage, or may have partially or fully-overlapping areas of coverage. For example, one wireless network may effectively be co-located with another, perhaps by siting their respective base stations at the same sites or in the same housings.
The above is only one general type of wireless network. In this specification, the term wireless network also encompasses a wireless sensor network (WSN) in which the nodes are sensors of some kind, configured to at least act as transmitters (and sometimes also act as receivers). In such a network, an entity called a “sink” gathers information from the sensors, and has a role analogous to the base station of a wireless communication network. One special form of wireless sensor network is a so-called Body Area Network or BAN, in which sensors are placed at one or more positions on or in living bodies for the purpose of monitoring medical parameters or bodily activity. Two forms of BAN are MBAN or Medical BAN for use in hospitals and other health-related applications, and Wireless BAN or WBAN, this more general designation also extending to security applications for example.
The concept of “interference temperature” has been proposed for use in managing interference among network nodes such as clusters of BSs and/or UEs. This concept uses the fact that it is the interference level at the affected receiver, rather than at the transmitter causing the interference, which is important to determine the impact of a transmission on other networks. By limiting the total interference experience at a given receiver, it is possible to allow transmitters to operate in frequency bands (sub-channels or chunks) already allocated to other transmitters whilst protecting the receivers from undue interference. In practice, it is unrealistic to expect each transmitter to obtain the necessary information for estimating how their emissions would affect the interference temperature at a given receiver. Nevertheless, the concept of “interference temperature” is useful for classifying the level of interference experienced in particular frequency bands by receivers and groups (e.g. clusters) of receivers.
Given the potential for interference as already noted, interference management, also referred to below as interference mitigation, is essential for allowing efficient sharing and utilization of spectrum between BSs and clusters in wireless networks. However, there is a conflict between the desire for distributed management, permitting spectrum allocation to be rapidly varied in response to changing conditions, and the need for centralized management to ensure coordination among clusters and between networks.